I. Field of the Invention
This invention relates generally to a method and related apparatus for controlling the operation of a press brake system for bending a bar, tube, sheet or other workpiece to a required angle during a metal forming process.
II. Background Information
Operation of a press brake system to bend a sheet or workpiece, such as a press brake, to a requested bend angle typically includes a series of manual press setup steps. The steps involved in press setup include the step of placing a first workpiece over a die of the press in a manner such that, when the ram of the press is operated, being brought into contact with the first workpiece, the workpiece is bent to a first bend angle. The first bend angle to which the workpiece is bent is a function of various parameters including the position in the die to which the ram travels when brought into contact with the first workpiece.
Accordingly, press setup also includes the step of selecting and setting the position, into the die, to which the ram of the press travels when operated, this position setting being performed in an effort to obtain a first bend angle equal in size to the requested bend angle.
After the above-mentioned steps have been performed, press setup continues with the step of operating the ram to travel to the selected position to bend the first workpiece. The first workpiece having been bent, the size of the first bend angle is then measured. The difference between the measured first bend angle and the requested bend angle is obtained.
In accordance with the difference between the first and the requested bend angles, a next travel position for the ram is selected and the travel position for the ram is reset. The travel position is reset in an effort to control the bend angle of a second workpiece to more nearly approach the requested bend angle. Thereafter, the setup process continues with the steps of placing the second workpiece over the die and operating the ram to travel to the next selected position to bend the second workpiece. The size of the second bend angle is then measured and compared with the requested bend angle.
In accordance with the difference between the second and the requested bend angles, selection and manual resetting of the travel position of the ram is again performed. The travel position is reset to another next selected position for achieving the requested bend angle using a third workpiece.
In the iterative manner described above, third and successive workpieces are bent by the press until the ram of the press is operated from a correct selected position to achieve a bend angle for a successive workpiece which is equivalent to the requested bend angle. Once this equivalence has been achieved, press setup is complete, and a batch of identical workpieces to be bent to the same requested bend angle are bent by operating the ram to the corrected position. The above-described setup steps are repeated whenever, due to any changes in press brake performance, the batch of identical sheets are no longer being bent to the requested angle. In such an event, each of the manual setup steps described is again performed.
Performing the above-described bending and measuring, and manual setting and resetting steps requires significant amounts of time, causes the press setup to be slow and thereby generally slows the process of bending workpieces. Accordingly, several approaches have been tried to automatically control the operation of a brake press to increase the rate at which workpieces may be bent to a requested bend angle.
One proposed approach for controlling press operation which has been experimented with is the approach referred to as "adaptive bending." According to the adaptive bending approach, a ram is equipped with sensors for measuring air pressure between the ram and the workpiece being bent. In accordance with the air pressure and certain information regarding air pressure and bend angle relationships, control apparatus, connected to the ram, die and other press apparatus, sets the travel position of the ram. The adaptive bending approach, and the air pressure information used in adaptive bending, have yielded marginally accurate controlled bending results.
Another proposed approach utilizes a control apparatus of a press including a folding die and an articulating die base. The fold of the die and the position of the base are automatically controlled to achieve a requested bend angle. This system, however, lacks the level of sensitivity desired.
Yet another proposed approach for controlling operation of the press is the "force/displacement" approach. A force/displacement control system operates to set the ram travel position according to the predicted force exerted by the ram when the ram, traveling to a selected position, is brought in contact with a workpiece of a given size and having specific physical properties. Accurate adjustments are performed by this control system only within a limited force range and with specific materials.